1. Field of the Invention
The present invention relates to a lift-variable valve-operating system for an internal combustion engine, comprising: subsidiary cams which are swingably supported on a movable support shaft capable of being displaced within a plane perpendicular to a rotational axis of a valve-operating cam, and which are swung following the valve-operating cam; and rocker arms each operatively connected to an engine valve and operated following the subsidiary cams, operating characteristics including a lift amount of the engine valve being changed by displacing the movable support shaft.
2. Description of the Related Art
Published Japanese Translation No. 2004-521234 of PCT Application No. PCT/EP2002/004332 and German Patent Application Laid-open No. 10237104 disclose lift-variable valve-operating systems, in which rocker arms operatively connected to engine valves are swung by subsidiary cams swung by valve-operating cams, and the lift amount of the engine valves and the timing for opening and closing the engine valves are changed by displacing engine valves and the timing for opening and closing the engine valves are changed by displacing fulcrums of the subsidiary cams.
However, in the systems disclosed in the above publications, each of the rocker arms is swingably supported at one end thereof by a hydraulic tappet mounted in a cylinder head, but the subsidiary cams are supported by a member different from the cylinder head, leading to a possibility that the position of abutment of the subsidiary cam against the rocker arm may be changed due to a thermal influence even under the same operating conditions. The position of abutment of the subsidiary cam against the rocker arm may be also changed due to an assembling error and a cumulative dimensional error caused by the interposition of a plurality of different members between a swinging fulcrum for the rocker arm and a swinging fulcrum for the subsidiary cam. Thus, in a valve-operating system designed to change the lift amount of an engine valve, there is a possibility that, particularly in a low-lift state, the proportion of the change in the abutment position with respect to the lift amount may be increased to exert a significant influence to the control of the lift amount.